White Paper Title: 
Oceanic fixed nitrogen sinks and associated bacterial communities in the hydrothermal vents of the Juan de Fuca Ridge

Nitrogen is a building block of proteins and is thus an essential macronutrient for all organisms. Oceanic N sinks that remove bio-available N ultimately affect both photosynthetic and chemosynthetic primary productivity. A better understanding of bacterially-mediated N-cycle dynamics is thus essential to understanding metabolic processes taking place in the subsurface biosphere of hydrothermal vent systems. Furthermore, the relative importance of the two main N-elimination pathways (i.e. denitrification and anammox) in the global ocean is still a matter of debate and has never been explored in hydrothermal systems.

For my Ph. D research at the University of Victoria (British Columbia, Canada) I am studying the nitrogen (N) cycle and the related microbial community in subsurface hydrothermal systems of the Juan de Fuca Ridge (North-East Pacific Ocean) by applying a combination of biogeochemical and molecular biology methods to sampled vent fluids.

I began my project by analyzing the isotopic composition of dissolved inorganic N (nitrate and ammonium). These findings inform us about the biological transformations related to the N-cycle in hydrothermal vents. I have also measured rates of several N-removal processes (denitrification, anaerobic ammonium oxidation (anammox) and dissimilative nitrate reduction to ammonium (DNRA)) using labelled 15N incubation techniques. The second phase of my study involves using molecular biology techniques to identify the various organisms involved in the N-cycle. I am using 16S ribosomal RNA (16S rRNA) sequence information (anammox) as well as targeting specific functional genes (i.e. genes encoding the enzymes necessary for N-removal processes, i.e. denitrification and DNRA).  This approach is allowing me to characterize the diversity and abundance (using q-PCR assays) of the microbial community and identifying the organisms responsible for major N-removal transformations in hydrothermal vent systems.

I expect to contribute substantially to my working group during the Ridge 2000 Program at the 2010 Community Meeting by bringing new essential information about N-cycling in hydrothermal vent systems and writing a part of a potential paper on the subject. To the best of my knowledge, I will be the only scientist working on bio-available N-removal in hydrothermal vents at the meeting. For several reasons (listed below), a section on bio-available N is indispensable in a synthesis paper about biogeochemical processes in hydrothermal vents. My combined biogeochemical and molecular biology approach will allow me to contribute a comprehensive synthesis of N sinks in hydrothermal vents to the group discussions and to the preparation of a synthesis manuscript. I also provide first measurements of the isotopic composition of dissolved inorganic nitrogen, rates of major N-elimination processes and characterization of the diversity and abundance of the related microbial community.

So far, geochemical and microbiological data documenting N-cycling in hydrothermal fluids have been extremely scarce because of sampling and analytical limitations. This Ph. D project is unique and only possible because of the numerous collaborations with scientists from around the world (i.e. University of Washington (USA), University of Basel (Switzerland), Max Planck Institute (Germany), University of British Columbia (Canada)) that allowed sampling pure hydrothermal vent fluids and several specific analyses to be done.